1. Field of the Invention
The present invention relates to an optical recording medium for recording information using heat caused by a converged light beam, and particularly relates to an optical recording medium having land and groove tracks.
2. Description of the Related Art
In recent years, optical recording medium dedicated to recording information have played an important role for storing voice information data, video information data, and the like, because of their large capacity. An optical recording medium having a larger capacity has been in demanded. In order to satisfy this demand, the recording density of a recording medium needs to be increased. Information density of an optical recording medium is determined by the pitch of the information tracks and the information density in the direction of the tracks, namely the linear density of information. In order to improve the information density on the optical recording medium, the pitch of the track needs to be narrower, or the linear density needs to be larger.
A typical example of a conventional optical recording medium has a small spiral grooved track of 0.8 .mu.m width and 1.6 .mu.m pitch formed on a resin disk substrate. Then, a thin film of a phase change type material consisting of three elements, such as Te, Sb, and Ge as its main constituents is formed on the surface of the substrate by a sputtering method or the like, and a protection layer is formed on the thin film (as described An Japanese Laid-Open Patent Publication No. 60-121550). A stamper is made based on a master disk on which the groove track is cut, and numerous resin substrates replicated from the master disk are produced by injection or the like.
Since this conventional optical recording medium is constructed to record information on the groove track, the track width becomes narrower as the track pitch is made narrower, and production of the master disk or replication of the resin substrate thus becomes difficult. Moreover, when the information recorded on the track is reproduced, since the power of reflected light or transmitted light from the track decreases, the quality of the reproduced signal becomes degraded.
One of the purposes for providing the groove track is to control the light beam so that it is exactly positioned on the track by detecting a deviation signal indicating a deviation of the light beam, which is radiated on the optical recording medium, with regard to the track. Generally, the deviation signal of the light beam on the optical recording medium with regard to the track, namely a tracking error signal, is detected by a push-pull method. In the push-pull method, a far field pattern of the reflected or transmitted light from an optical recording medium is detected by a divided photodetector having two photosensitive regions, and a deviation of the light beam with regard to the track on the optical recording medium is detected according to a difference between the photoelectric currents detected at both of the photosensitive regions. The width and pitch of the track determine the intensity and dynamic range of the tracking error signal. AS the track width is made narrower so as to reduce the intensity of the pitch, the amplitude of the tracking error signal becomes smaller and the dynamic range becomes narrower, the quality of the tracking error signal thus becomes degraded. As a result, the tracking control becomes unstable, and a jumping of tracks tends to occur when an external shock, such as shaking or hitting, is applied.
In order to solve these problems, it is proposed that a spiral groove track is formed in the radial direction of an optical recording medium so as to attain a high information density by recording information also on the land track between adjacent turns of the groove track (as shown in Japanese Laid-Open Patent Publication No. 57-50330). In this optical recording medium, when the pitch of the groove or land track is 1.6 .mu.m, the distance between the groove and land tracks, namely the track pitch, is half the pitch of the groove or land track, or 0.8 .mu.m. However, the amplitude of the tracking error signal does not become smaller and the dynamic range does not become narrower.
An identification information for identifying positions is necessary to record information on a desired position or to search for the desired information. In order to provide the identification information for identifying positions of recording regions on both the groove and land tracks, since the pitch of the pits for the identification information in the radial direction is 0.8 .mu.m, the pit width for the identification information needs to be a half of or less than the width of the groove and land tracks. This makes it difficult to produce a master disk and to replicate resin, substrates. Furthermore, three cutting light beams: a light beam for cutting the groove track; a light beam for cutting the identification information on the land track and a light beam for cutting the identification information on the groove track are required to produce the master disk, so a cutting machine consequently becomes complex and expensive.
Moreover, since this optical recording medium has two spiral tracks (i.e., the groove and land tracks), it takes time for a reading head to move from the groove track to the land track, and vice versa. Thus, there is a problem that information can not be recorded continuously.